Breakout stars in Hollywood usually fit a certain aesthetic but Aussie actress-comedienne, Rebel Wilson, 27, is something of an anomaly. She's making a name for herself in part due to her plus-size screen presence, maximising the extra kilos to her advantage.

Since her role in Bridesmaids, Wilson has found herself on the employment treadmill. Her scene-stealing performance in the ensemble, What to Expect When You're Expecting led to a starring role in Pitch Perfect, and she will next appear in Pain and Gain, due for release next year.

"Weirdly, I get a lot of work where people tell me they don't want me to lose weight," she says.

Wilson was the first to be cast in in Pitch Perfect, a movie about competitive college a capella groups.

She plays Fat Amy - a name at odds with her new off-screen role as spokesperson for Jenny Craig Australia. Pitch Perfect producers feared weight loss would affect the storyline, and she was therefore contractually obligated to remain the same size.

"I was not permitted to go outside of 2kg," she confirms.

For many actors, playing a character called Fat Amy might be taken offensively. However, Wilson says, "Funny enough, I played a character named Fat Mandi [in Australian sketch show The Wedge], so if I hadn't had that background with this kind of thing, maybe I would have reacted differently when I got the script.

"But also, this is a girl who's super-confident in herself, and the writing is really funny, so when I read it I thought, 'Oh my God, I have to play this'. It was like when I read Melissa McCarthy's role in the Bridesmaids script, I said, 'Whoever gets to play this is going to be super-funny'."

A former law student ("I used to watch Ally McBeal and I thought being a lawyer seemed really cool, especially that they got to sing at the end of the week at the piano bar"), Wilson grew up in Sydney with her similarly colourfully-named siblings: Liberty, Ryot, and Annachi. Their parents were in the dog show business.

"I would be dragged every weekend to a dog show and I was forced to be a junior handler. We had competitions all the time and I really didn't like it. I found running around with the dogs, the dorkiest thing ever, so when I was 12 or 13 and I was old enough to stay home, I did."

After going to drama school, she won an scholarship to train with Second City, the famed Chicago improv group. Returning home, she became a regular on local tv comedies including Bogan Pride in which she played the role of an obese teenager named "Jennie Cragg".

"Some people think success is overnight. I suppose, considering I came from Australia, it has been pretty quick. But I have a background in stand-up and improv so I've really had to prove myself. It's not like I was plucked out of nowhere to be in these movies. When I was just a girl in Sydney, no one thought, 'Oh, she's going to be a movie star'. No one. I had to get by with actual skill and talent."

Wilson hasn't let her increasing international profile go to her head - her nearest and dearest won't let her.

"My family will be like, 'You aren't funny and your accent wasn't that good'," she laughs. "My grandmother is always saying, 'Why couldn't you wear something more flattering?' So they are constantly putting me down."

Wilson agrees she might have to shed some kilos for a role one day but right now she's benefitting from being able to stand out in ensembles like Pitch Perfect's.

And like most comedians, there's usually a dark side lurking behind the humour.

"Well, I've experienced tragedy and I turned that into comedy. I almost died when I was in Africa several years ago. I contracted malaria when I was there as a Rotary Youth Ambassador for Australia and I didn't take my pills. I hallucinated that I was an actress and that's where this career started. I'm really thankful for that," she says. "For a comedienne, you have to have a little tragedy or a dark side, just not too much. Otherwise it's too disruptive."